Metal ion-assisted carboxyl-containing covalent organic frameworks for the efficient removal of Congo red

Covalent organic frameworks (COFs) have been utilized as molecular sieves to adsorb or remove or separate a wide range of substances. Herein, a new carboxyl-containing COF (COF-COOH) is fabricated from the polymerization of 1,3,5-triformylphloroglucinol (TP) and 4,4′-diamino-[1,1′-biphenyl]-3,3′-dicarboxylic acid (DBA). COF-COOH displays good adsorption performance on Congo red (CR) through hydrogen bonds and π-π stacking interactions. Through post-modification with Ca 2+ /Ni 2+ ions, the adsorption capacity of COF-COOCa/COF-COONi to CR is improved, which is due to the coordinated metal cations having a positive contribution to the electrostatic interactions. At 25 °C, the maximum adsorption amount of COF-COOCa and COF-COONi to CR is 704.23 mg g −1 and 781.25 mg g −1 , respectively. The removal efficiency of COF-COOCa to CR is 95% and that of COF-COONi is 96%. This demonstrates that the new metal ion-assisted COFs are viable adsorbents to remove dye pollutants, which are harmful to the environment and to human health, from wastewater. Covalent organic frameworks (COFs) have been utilized as molecular sieves to adsorb or remove or separate a wide range of substances.